Ok Front O2s reconnected, rear O2s left disconnected. Key on, all four sensors reading .4v. I'm assuming that's baseline? The rears never changed.

Started the truck. Fronts read .4v at first, but voltage quickly started to drop. Within the first 60 seconds they had both dropped to 0v (rears still reading .4v) and Torque says, under Component Status, "Fuel System Status: Open loop due to system failure."

I left the key on and engine off while I typed this and both sensors have gone back up to .4v.

I'm going to disconnect the O2 sensor that had 12v on pin 1 and see if that makes any change.

 

Tried it again. Same deal except the disconnected passengers side O2 also stayed at .4v now.

Drivers side dropped to .3v and it immediately kicked to "Open loop due to system failure". It was still reading and I watched it drop to .2, back to .3, back to .2, .1, then 0v.

 

Related side note, though not immediately pertinent; I just ordered two Walker O2 sensors from RockAuto. They had a wholesaler closeout, only one remaining for $19. I got both for $67 shipped.

Another question; is there another difference between the front and rear O2s other than the plug? Could I switch the plugs and replace the one known bad rear sensor with one of the old front sensors which might be fine?

 

It sounds like you are having the same problem I did?
Check the you have 12 volts on both sides of the brown with pink tracer wire on both sides of the grey connector with the key turned on.
And make sure none of your pins pushed back in your connectors at the O2 sensor.

 

Confirmed 12v on the brown/pink wire and confirmed no pins pushed back.

 

The voltage drop off is in my experience can be two things:
1) bad O2's. Had what you describe multiple times, why I went with walkers
2) Not fully connected. shove those connectors together until they squeal like a pig. The minute the sensors heat up and the block does, poor connection will make them drop off line.

 

Following this thread. I have two new dead O2 sensors on my Disco. Live data stream shows 0 volts on both upstream sensors and open loop.

 

Matt, yeah. I originally wanted to go with the Walkers, but I ended up with the Bosch sensors because they were the only one's Advance could get next day. I'm going to return them as defective when the Walkers come in.

I've definitely squeezed them together real d*mn tight, so that shouldn't be it I don't *think*.

Fingers crossed that those Walker sensors fix the issue. I'll update when they come in and I test them.

 

I'm gonna go ahead and ask. Can anyone confirm that those readings on the harness side of the O2 plugs are correct?

 

Alright, an update. I got the Walker O2 sensors installed and I'm getting readings from them. The miss is pretty well gone. I think the remaining miss might be an issue with my snorkel because it's only at 70+ mph; it's not RPM or throttle dependent. I'm going to be doing more testing on that soon.

Now, As I said I am getting readings from the O2 sensors (usually around .8v on both) and it is running a lot smoother, but Torque is still telling me that it's still going to open loop "due to system failure" and I'm still getting check engine codes for all four O2s and their heater circuits, despite the fact that I'm reading voltage off of all of them through the OBD2 port/Torque app and despite the fact that the truck is running exponentially better with the new sensors. Befuddled I am.

I am going to try resetting my adaptive values to see if that changes anything. Maybe the ECU is just locked up somehow and isn't capable of actually deleting those codes right now.

Another code popped up today for the evap system. Purge valve or gas cap code. Great. That's only the second purge valve I've had on the thing.

If anyone has any ideas on why the computer is reading the O2 sensors but it's throwing codes for not reading the O2 sensors, I'd love to hear them.